Influence of elevated temperature on bond performance of basalt FRP bars with steel fiber-reinforced concrete

Concrete type	Compressive strength (MPa)		Splitting tensile strength (MPa)
Concrete type	Ambient temperature	200 °C	Ambient temperature	200 °C
PC	42.0 ± 2.8	41.4 ± 3.2	3.8 ± 0.2	3.7 ± 0.3
FRC	46.0 ± 3.1	45.2 ± 3.3	6.0± 0.5	5.8 ± 0.6

Beam-end test specimen details (all dimensions are in mm).

Table 2

Test matrix.

S. No.	Specimen ID	Volume fraction of steel fibers	Type of test rebar	Diameter of rebar (mm)	Exposure temperature	No. of test specimens
1	PCSB-A	0	Steel	12	Ambient temperature	2
2	PCSB-100	0	Steel	12	100°C	2
3	PCSB-200	0	Steel	12	200°C	2
4	FRCSB-A	1%	Steel	12	Ambient temperature	2
5	FRCSB-100	1%	Steel	12	100°C	2
6	FRCSB-200	1%	Steel	12	200°C	2
7	PCBB-A	0	BFRP	12	Ambient temperature	2
8	PCBB-100	0	BFRP	12	100°C	2
9	PCBB-200	0	BFRP	12	200°C	2
10	FRCBB-A	1%	BFRP	12	Ambient temperature	2
11	FRCBB-100	1%	BFRP	12	100°C	2
12	FRCBB-200	1%	BFRP	12	200°C	2
					Total = 24

Temperature–time variation followed in heating and cooling.

Table 3

Summary of study results.

Specimen ID	Peak force (kN)	Average bond strength (MPa)	Slip at peak load (mm)	Residual bond stress (MPa)	Failure mode*
PCSB-A	43.9 ± 2.40	19.3 ± 1.05	2.895 ± 0.12	2.9 ± 0.14	P & S
PCSB-100	42.8 ± 2.91	18.9 ± 1.29	3.200 ± 0.13	2.3 ± 0.16	P & S
PCSB-200	32.5 ± 1.84	14.4 ± 0.81	3.445 ± 0.15	7.9 ± 0.54	P & S
FRCSB-A	40.4 ± 2.51	17.9 ± 1.11	1.540 ± 0.1	3.6 ± 0.28	P
FRCSB-100	39.3 ± 3.10	17.4 ± 1.37	1.615 ± 0.12	4.4 ± 0.28	P
FRCSB-200	32.9 ± 2.37	14.5 ± 1.05	2.835 ± 0.24	4.4 ± 0.35	P
PCBB-A	37.5 ± 1.58	16.6 ± 0.7	1.955 ± 0.09	5.0 ± 0.28	P & S
PCBB-100	41.7 ± 2.42	18.4 ± 1.07	2.735 ± 0.15	1.8 ± 0.13	P & S
PCBB-200	40.7 ± 2.46	18.0 ± 1.09	2.865 ± 0.19	3.2 ± 0.28	P & S
FRCBB-A	32.9 ± 2.13	14.5 ± 0.94	1.630 ± 0.08	3.6 ± 0.25	P
FRCBB-100	40.7 ± 3.34	18.0 ± 1.48	2.295 ± 0.12	8.7 ± 0.64	P
FRCBB-200	38.5 ± 3.02	17.0 ± 1.34	1.935 ± 0.13	9.5 ± 0.78	P & S

Failure modes of rebars embedded in PC and FRC.

Comparison of bond strength of rebars embedded in PC and FRC after exposure to different temperatures: (a) steel vs BFRP bars in PC; (b) steel vs BFRP bars in FRC; (c) steel bars in PC vs FRC; and (d) BFRP bars in PC vs FRC.

Bond stress–slip curves of steel and BFRP rebars embedded in PC and FRC after exposure to different temperatures: (a) steel bar embedded in PC; (b) BFRP bar embedded in PC; (c) steel bar embedded in FRC; and (d) BFRP bar embedded in FRC.

Table 4

mBPE model parameters obtained by curve fitting.

Concrete type	Rebar type	Exposure temperature	Model parameters
Concrete type	Rebar type	Exposure temperature	$α$	$ρ$	$r$	s _max
PC	Steel rebar	Ambient temperature	0.88	1.500	0.15	2.895
		100°C	0.91	0.750	0.12	3.200
		200°C	0.96	2.300	0.55	3.445
	BFRP rebar	Ambient temperature	0.69	0.124	0.300	1.955
		100°C	0.72	0.340	0.100	2.735
		200°C	0.85	0.550	0.18	2.865
FRC	Steel rebar	Ambient temperature	0.55	0.190	0.20	1.540
		100°C	0.62	0.205	0.25	1.615
		200°C	0.72	0.380	0.30	2.835
	BFRP rebar	Ambient temperature	0.70	0.100	0.25	1.630
		100°C	0.72	0.110	0.48	2.295
		200°C	0.88	0.105	0.56	1.935

Table 5

Equations of bond model parameters as a function of exposure temperature.

Embedded in PC*	Embedded in FRC*
	Steel rebars
$α = 0.0005 T + 0.867$ (R ² = 0.99)	$α = 0.001 T + 0.525$ (R ² = 0.99)
$ρ = 0.0001 T^{2} - 0.0282 T + 2.114$ (R ² = 1.00)	$ρ = 9 \times 10^{- 6} T^{2} - 0.0009 T + 0.21$ (R ² = 1.00)
$s_{\max} = 0.0031 T + 2.844$ (R ² = 0.98)	$s_{\max} = 0.0077 T + 1.167$ (R ² = 0.86)
$r = 0.0006 T + 0.1885$ (R ² = 0.99)	$r = 0.0006 T + 0.1885$ (R ² = 0.99)
	BFRP rebars
$α = 0.0009 T + 0.652$ (R ² = 0.93)	$α = 0.0011 T + 0.652$ (R ² = 0.89)
$ρ = 0.0024 T + 0.0762$ (R ² = 0.99)	$ρ = 2 \times 10^{- 5} T + 0.102$ (R ² = 1.00)
$s_{\max} = 0.005 T + 1.978$ (R ² = 0.79)	$s_{\max} = 0.0015 T + 1.796$ (R ² = 0.95)
$r = 0.0017 T + 0.244$ (R ² = 0.88)	$r = 0.0017 T + 0.244$ (R ² = 0.88)

*For quadratic models, R ² is unity, as there are only three points.

Modified mBPE model vs experimental bond stress–slip curves of rebars embedded in PC at ambient and elevated temperatures: (a, c, and e) steel rebars exposed to ambient temperature, 100°C, and 200°C; and (b, d, and f) BFRP rebars exposed to ambient temperature, 100°C, and 200°C.

Modified mBPE model vs experimental bond stress–slip curves of rebars embedded in FRC at ambient and elevated temperatures: (a, c, and e) steel rebars exposed to ambient temperature, 100°C, and 200°C; and (b, d, and f) BFRP rebars exposed to ambient temperature, 100°C, and 200°C.

Table 6

Codes and researchers’ models for bond strength of steel rebars embedded in concrete*.

Code/Researcher	Model for ambient temperature	Model for elevated temperature
ACI 408R-03 [26]	$τ_{\max, 20} = 20 \frac{\sqrt{f_{c}^{'}}}{d_{b}}$	NA
CEB-FIP Model Code [34]	$τ_{\max, 20} = 2 \sqrt{f_{c}^{'}}$	NA
CEB-FIP Model Code [35]	$τ_{\max, 20} = 2.5 \sqrt{f_{c}^{'}}$	NA
Huang [36]	$τ_{\max, 20} = 2.5 \sqrt{f_{c}^{'}}$	$τ_{\max, T} = \begin{array}{l} 2.5 \sqrt{f_{c}^{'}} for 20 \leq T \leq 400 {}^{\circ}C \\ f_{c}^{'} 0.4 for 400 < T \leq 800 {}^{\circ}C \\ 0 for T > 800 {}^{\circ}C \end{array}$
Lublóy and György [37]	$τ_{\max, 20} = 2 \sqrt{f_{c}^{'}}$	$τ_{\max, T} = \begin{array}{l} 2 \sqrt{f_{c}^{'}} 1.0 - \frac{0.22}{360} (T - 20)) for 20 \leq T \leq 380 {}^{\circ}C \\ 2 \sqrt{f_{c}^{'}} 0.78 - \frac{0.75}{270} (T - 380)) for 380 < T \leq 650 {}^{\circ}C \\ 0.06 \sqrt{f_{c}^{'}} for T > 650 {}^{\circ}C \end{array}$

* $τ_{\max, 20}$ = bond strength at room temperature (MPa); $f_{c}^{'}$ = specified compressive strength of concrete (MPa); $d_{b}$ = diameter of rebar (mm); $τ_{\max, T}$ = bond strength at elevated temperature (MPa); T = exposure temperature (°C); NA = not available model.

Table 7

Prediction of bond strength of steel rebars using codes and researchers’ models*.

Specimen ID	Bond strength model
	ACI 408R-03 [26]		CEB-FIP model code [34]		CEB-FIP model code [35]		Huang [36]		Lublóy & György [37]
	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$
PCSB-A	10.80	0.56	12.96	0.67	16.20	0.84	12.96	0.67	16.20	0.84
PCSB-100	NA	—	NA	—	NA	—	12.33	0.65	16.20	0.86
PCSB-200	NA	—	NA	—	NA	—	11.54	0.80	16.20	1.13
FRCSB-A	11.3	0.63	13.56	0.76	16.96	0.95	13.56	0.76	16.96	0.95
FRCSB-100	NA	—	NA	—	NA	—	12.90	0.74	16.96	0.97
FRCSB-200	NA	—	NA	—	NA	—	12.07	0.83	16.96	1.17

* $τ_{\max, TH}$ = predicted bond strength; $τ_{\max, EXP}$ = experimental bond strength; NA = not available results.

Comparison of predicted and experimental bond strength for: (a) steel rebars embedded in PC and (b) steel rebars embedded in FRC.

Table 8

Codes and researchers’ models for bond strength of BFRP bars embedded in concrete*.

Code/Researcher	Model for ambient temperature	Model for elevated temperature
ACI 440.1R-15 [8]	$τ_{\max, 20} = 0.083 \sqrt{f_{c}^{'}} 4.0 + 0.3 \frac{C}{d_{b}} + 100 \frac{d_{b}}{ℓ_{e}})$	NA
CAN/CSA-S6-14 [11]	$τ_{\max, 20} = \frac{0.4 \sqrt{f_{c}^{'}} d_{c s}}{0.45 π d_{b} k_{1} k_{4}}$	NA
JSCE [38]	$τ_{\max, 20} = \frac{0.318 + 0.795 \frac{c}{d_{b}}}{\frac{3.2}{\sqrt{f_{c}^{'}}} - \frac{53.2}{f_{fu}}}$	NA
Model (1) – El-Gamal [39]	$τ_{\max, 20} = 20.23 \frac{\sqrt{f_{c}^{'}}}{d_{b}}$	$τ_{\max, T} = 20.23 \frac{\sqrt{f_{c}^{'}}}{d_{b}} - 0.015 Δ T \sqrt{t}$
Model (2) – El-Gamal [39]	$τ_{\max, 20} = 2.5 \sqrt{f_{c}^{'}}$	$τ_{\max, T} = 2.5 \sqrt{f_{c}^{'}} - 0.015 Δ T \sqrt{t}$
Özkal et al. [40]	$τ_{\max, 20} = 0.083 \sqrt{f_{c}^{'}} 4.0 + 0.3 \frac{C}{d_{b}} + 100 \frac{d_{b}}{ℓ_{e}})$	$\begin{array}{l} τ_{\max, T} = γ_{f} η_{f} f (T) 20 \leq T \leq 600 {}^{\circ}C \\ γ_{f} = \frac{τ_{\max, FRP, 20}}{τ_{\max, steel, 20}} \\ η_{f} = \frac{1473 - T}{1,450} \\ f (T) = 0.981 τ_{\max, steel, 20} 1 - \frac{T}{1,450}) \\ τ_{\max, steel, 20} = 20 \frac{\sqrt{f_{c}^{'}}}{d_{b}} \\ τ_{\max, FRP, 20} = 0.083 \sqrt{f_{c}^{'}} 4.0 + 0.3 \frac{C}{d_{b}} + 100 \frac{d_{b}}{ℓ_{e}}) \end{array}$

* $τ_{\max, 20}$ = bond strength at ambient temperature (MPa); $f_{c}^{'}$ = specified compressive strength of concrete (MPa); C = smaller of the cover to the center of the BFRP rebar or 1.5 times of the center-to-center spacing of the rebars (mm) (= 44 mm used in this study); c = $d_{b}$ = diameter of rebar (mm) (= 12 mm used in this study); $ℓ_{e}$ = embedment length of BFRP rebars (mm) (= 60 mm used in this study); d _cs = smaller of distance from the closest concrete surface to the center of the BFRP rebars and 2/3 of the center-to-center spacing of the BFRP rebars (mm) (= 44 mm used in this study); k ₁ = rebar location factor = 1.0; k ₄ = rebar surface factor = 0.8; c = smaller of concrete cover to the BFRP rebar and 1.5 times of the rebar spacing (mm) (= 38 mm used in this study); f _fu = tensile strength of BFRP rebars (MPa); $τ_{\max, T}$ = bond strength at elevated temperature (MPa); ΔT = difference between exposure temperature (T) and ambient temperature (20°C); t = exposure duration in hours (= 3 h used in this study); $τ_{\max, FRP, 20}$ = bond strength of BFRP rebar at room temperature (MPa); $τ_{\max, steel, 20}$ = bond strength of steel rebar at room temperature (MPa); T = exposure temperature (°C); NA = not available model.

Table 9

Prediction of bond strength of BFRP rebars using codes and researchers’ models.

Specimen ID	Bond strength model
	ACI 440.1R-15 [8]		CAN/CSA-S6-14 [11]		JSCE [38]		Model (1) – El-Gamal [39]		Model (2) – El-Gamal [39]		Özkal et al. [40]
	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$	$τ_{\max, TH}$ (MPa)	$\frac{τ_{\max, TH}}{τ_{\max, EXP}}$
PCBB-A	13.50	0.81	8.40	0.51	6.47	0.39	10.93	0.66	16.20	0.98	13.50	0.81
PCBB-100	NA	—	NA	—	NA	—	8.85	0.48	14.12	0.77	11.68	0.63
PCBB-200	NA	—	NA	—	NA	—	6.25	0.35	11.53	0.64	10.02	0.56
FRCBB-A	14.13	0.97	8.80	0.61	6.81	0.47	11.43	0.79	16.96	1.17	14.13	0.97
FRCBB-100	NA	—	NA	—	NA	—	9.36	0.52	14.88	0.83	12.22	0.68
FRCBB-200	NA	—	NA	—	NA	—	6.76	0.40	12.28	0.72	10.49	0.62

* $τ_{\max, TH}$ = predicted bond strength; $τ_{max,EXP}$ = experimental bond strength; NA = not available results.

Comparison of predicted with experimental bond strength for: (a) BFRP rebars embedded in PC and (b) BFRP rebars embedded in FRC.

References

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DOI: https://doi.org/10.2478/msp-2025-0050 | Journal eISSN: 2083-134X (formerly 2083-124X) | Journal ISSN: 2083-1331

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Language: English

Page range: 221 - 242

Submitted on: Aug 17, 2025

Accepted on: Dec 14, 2025

Published on: Dec 31, 2025

Published by: Wroclaw University of Science and Technology

In partnership with: Paradigm Publishing Services

Keywords:

Bond,

Beam-end test,

Basalt FRP rebars,

Fiber-reinforced concrete,

Elevated temperature

Related subjects:

Materials sciences,

Materials sciences, other,

Nanomaterials,

Functional and smart materials,

Materials characterization and properties

© 2025 Mohammed Abdulaziz, Husain Abbas, Hussein Elsanadedy, Aref Abadel, Tarek Almusallam, Yousef Al-Salloum, published by Wroclaw University of Science and Technology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Volume 43 (2025): Issue 4 (December 2025)

Influence of elevated temperature on bond performance of basalt FRP bars with steel fiber-reinforced concrete

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